Translation of 5' leaders is pervasive in genes resistant to eIF2 repression
ELIFE
Authors: Andreev, Dmitry E.; O'Connor, Patrick B. F.; Fahey, Ciara; Kenny, Elaine M.; Terenin, Ilya M.; Dmitriev, Sergey E.; Cormican, Paul; Morris, Derek W.; Shatsky, Ivan N.; Baranov, Pavel V.
Abstract
Eukaryotic cells rapidly reduce protein synthesis in response to various stress conditions. This can be achieved by the phosphorylation-mediated inactivation of a key translation initiation factor, eIF2. However, the persistent translation of certain mRNAs is required for deployment of an adequate stress response. We carried out ribosome profiling of cultured human cells under conditions of severe stress induced with sodium arsenite. Although this led to a similar to 4.5-fold general translational repression, the protein coding ORFs of certain individual mRNAs exhibited resistance to the inhibition. Nearly all resistant transcripts possess at least one efficiently translated uORF that repress translation of the main coding ORF under normal conditions. Site specific mutagenesis of two identified stress resistant mRNAs (PPP1R15B and IFRD1) demonstrated that a single uORF is sufficient for eIF2-mediated translation control in both cases. Phylogenetic analysis suggests that at least two regulatory uORFs (namely in SLC35A4 and MIEF1) encode functional protein products.
A Subunit of Eukaryotic Translation Initiation Factor 2 alpha-Phosphatase (CreP/PPP1R15B) Regulates Membrane Traffic
JOURNAL OF BIOLOGICAL CHEMISTRY
Authors: Kloft, Nicole; Neukirch, Claudia; von Hoven, Gisela; Bobkiewicz, Wiesia; Weis, Silvia; Boller, Klaus; Husmann, Matthias
Abstract
The constitutive reverter of eIF2 alpha phosphorylation (CReP)/PPP1r15B targets the catalytic subunit of protein phosphatase 1 (PP1c) to phosphorylated eIF2 alpha (p-eIF2 alpha) to promote its dephosphorylation and translation initiation. Here, we report a novel role and mode of action of CReP. We found that CReP regulates uptake of the pore-forming Staphylococcus aureus alpha-toxin by epithelial cells. This function was independent of PP1c and translation, although p-eIF2 alpha was involved. The latter accumulated at sites of toxin attack and appeared conjointly with alpha-toxin in early endosomes. CReP localized to membranes, interacted with phosphomimetic eIF2 alpha, and, upon overexpression, induced and decorated a population of intracellular vesicles, characterized by accumulation of N-(lissamine rhodamine B sulfonyl) phosphatidylethanolamine (N-Rh-PE), a lipid marker of exosomes and intralumenal vesicles of multivesicular bodies. By truncation analysis, we delineated the CReP vesicle induction/association region, which comprises an amphipathic alpha-helix and is distinct from the PP1c interaction domain. CReP was also required for exocytosis from erythroleukemia cells and thus appears to play a broader role in membrane traffic. In summary, the mammalian traffic machinery co-opts p-eIF2 alpha and CReP, regulators of translation initiation.
COA
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